Aureterocele
is a congenital saccular dilatation of the
terminal portion of the ureter. It may be orthotopic, inserting in the normal location or it may
be ectopic. Ectopicureterocele enter the bladder in an abnormal location,
such as the bladder neck or urethra. They typically arise from the upper
pole moiety of a duplicated collecting systemand are more common in the
pediatric population.

Ureteroceles occur in approximately 1 in
every 4000 children and occur most commonly in caucasions.
Females are affected 4-7 times more often than males.

Radiographically, ureteroceles
have a classic appearance known as the "cobra head deformity" and
resembles a snake's head bulging into the bladder. It is often best dected on excretory urography.

The most commonly
accepted theory behind ureterocele formation is
the obstruction of the ureteral orifice during
embryogenesis, with incomplete dissolution of the Chwalla
membrane. (The Chwalla membrane is a primitive,
thin membrane that separates the ureteral bud
from the developing urogenital sinus.) Failure of
this membrane to completely perforate during development of the ureteral orifice is thought to explain the occurrence
of aureterocele.

Abdominal film following contrast enhanced CT
scan shows excretion into two ureters on the
left (arrows). In the bladder, a characteristic filling defect (yellow arrow)
is seen known as the "cobra head" deforming which represents herniation of the dilated distal ureter
bulging into the bladder.

The "cobra head" is more easily seen
with the ureterocele flipped upside down and
magnified.

Just be glad this isn't in YOUR bladder.

(1) CT scan and (2) ultrasound through
pelvis in patient with known right ureterocele
who complains of new right flank and groin pain. Both US
and CT show a stone contained within the ureterocele
perhaps causing the patients pain from intermittent obstruction. On CT,
this stone is radiodense (arrow) and on
ultrasound, the stone demonstrates strong acoustic reflection (has a
bright interface) and posterior acoustic shadowing (it is black behind
the stone because all sound is being reflected at the stones interface).